Given, the projection of a line on x -axis is lr=9....(i) on y -axis is, ‌‌mr=12....(ii) on z-axis, ‌‌nr=8.....(iii) On squaring and adding Eqs. (i), (ii) and (iii), l2r2+m2r2+n2r2=81+144+64 (l2+m2+n2)r2=289 r2=289‌‌(∵l2+m2+n2=1) Distance r=17